PTM transmissions allow communication which is accomplished via a one-to-many connection, providing multiple paths from a single location to multiple locations. Point-to-multipoint is often abbreviated not only as PTM, but also as P2MP, PTMP, or PMP. In 3GPP, one example of PTM transmission is the so called Multimedia Broadcast Multicast Service (MBMS). In 3GPP2, MBMS is called BroadCast and MultiCast Service (BCMCS).
The MBMS feature is split into the MBMS bearer service and the MBMS user service. The MBMS bearer service provides delivery for two services: broadcast and multicast (MBMS allows the distribution of files over broadcast/multicast bearers and introduces shared radio broadcast/multicast bearers). The broadcast service can be received by any subscriber located in the area where the service is offered and multicast services can only be received by users who have subscribed to the service and have joined the multicast group associated with the service. According to MBMS, the unicast system for point-to-point (PTP) transmission is offloaded when multiple devices and users are interested in the reception of the file. That is, within the radio access network, MBMS integrates PTM bearers for broadcast/multicast in cells with a high number of group members with PTP bearers for unicast. In consequence, a service delivered over MBMS typically uses PTM transmission (broadcast/multicast transmission) within geographical areas (e.g., in cells) of high density of group members and PTP transmission within geographical areas (e.g., in cells) with a low number of group members. Both services broadcast and multicast are unidirectional, point-to-multipoint transmissions of multimedia data and can be applied to broadcast text, audio, picture, video usually from a Broadcast/Multicast Service Center (BMSC or BM-SC) to any user located within the designated service area. Thus, MBMS ensures delivery of applications such as mobile TV, radio broadcasting, file delivery and emergency alerts.
The MBMS user service is basically the MBMS service layer and offers a streaming and a download delivery method. The streaming delivery method is used for continuous transmissions such as Mobile TV services. The Real-time Transport Protocol (RTP) may be used for delivering the content data in the streaming delivery method. The download method is intended for “Download and Play” services. For delivering the content data in the download method, content data is normally transported using the File Delivery over Unidirectional Transport (FLUTE) protocol (RFC 3926). To increase the transmission reliability, an application layer Forward Error Correction (FEC) code may be used. In other words, the FLUTE protocol allows FEC protection of content files and it may use the Internet Engineering Task Force (IETF) FEC framework. Further, a file-repair service may be offered to complement the download delivery method.
In order to allow mobile terminals to save battery, the concept of session and file schedule has been introduced in MBMS. According to this concept, the mobile terminals which are interested in receiving content data are provided with a sufficiently precise schedule so that the mobile terminals only need to wake-up and tune-in at time of possible reception. Thus, a mobile terminal only wakes up when the service(s) of its interest is (are) transmitted, while it can sleep during the transmission of other services or when no service is transmitted. For example, session and scheduling may be implemented in MBMS in the distribution of software updates. Typically all devices of the same type (e.g. Galaxy S III, or iPhone®) are interested in the same software package. Another example would be pre-loading of YouTube clips. Here the interest is not device specific (all Android™ and iOS® devices can handle the YouTube clip), but more user-interest specific.
The intention of the file delivery schedule solution (TS 26.346, version 11.3.0) is to give mobile terminals a reception schedule at which the mobile terminals shall expect to receive the file. The intention is that the mobile terminals should only wake up during the described schedule to save battery. The more precise the schedule is, the more the battery drain is reduced.